Chemical weapon

A chemical weapon is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons, this can be any chemical compound intended as a weapon "or its precursor that can cause death, injury, temporary incapacitation or sensory irritation through its chemical action. Munitions or other delivery devices designed to deliver chemical weapons, whether filled or unfilled, are also considered weapons themselves."
Lethal chemical weapons include nerve agents and blister agents. Non-lethal chemical weapons include tear gases like CS gas and pepper spray and incapacitating agents like 3-Q/BZ. Chemical weapons are typically highly volatile, while some like VX are persistent. They may be unitary or binary, combining from precursors in situ. Toxin weapons, as complex biologically-produced chemicals, blur the line with biological weapons.
Lethal chemical weapons are considered weapons of mass destruction, alongside nuclear weapons, biological weapons, and radiological weapons. Under the OPCW definition, toxic agents are not chemical weapons when used for another of their properties e.g. the herbicide Agent Orange or the incendiary white phosphorus.
The history of chemical warfare dates from antiquity. Chemical weapons were first used on a large scale by most major powers in World War I, employing mustard gas, the choking agents phosgene gas and chlorine, and others, causing lung scarring, blindness, and death. During World War II, Nazi Germany used a commercial hydrogen cyanide blood agent trade-named Zyklon B to commit industrialised genocide against Jews and other populations in gas chambers. The Holocaust resulted in the largest death toll to chemical weapons in history. The Empire of Japan also used chemical warfare in China during the Second Sino-Japanese War, including mustard gas and lewisite.
Nazi Germany discovered nerve agents during the war, but did not use them for fear of Allied retaliation. In the Cold War, many countries stockpiled chemical weapons. The Soviet and United States chemical weapons programs became the first and second largest in world history, focusing on sarin, VX/VR, and mustard, primarily for battlefield use in Europe. Chemical weapons were repeatedly used in the Iran–Iraq War and Syrian civil war.
At the end of the Cold War, the 1993 Chemical Weapons Convention sought a legally binding, worldwide ban on the production, stockpiling, and use of chemical weapons and their precursors. Large-scale stockpile destruction efforts followed, with the US eliminating its arsenal by 2023. the treaty has 193 state parties; Syria and Russia are widely believed to have violated its prohibitions on stockpiling and use while Israel and North Korea remain non-parties. Small research quantities are treaty-permitted as part of CBRN defense.

Use

Chemical warfare involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from nuclear warfare and biological warfare, which together make up NBC, the military initialism for Nuclear, Biological, and Chemical. None of these fall under the term conventional weapons, which are primarily effective because of their destructive potential. Chemical warfare does not depend upon explosive force to achieve an objective. It depends upon the unique properties of the chemical agent weaponized.
A lethal agent is designed to injure, incapacitate, or kill an opposing force, or deny unhindered use of a particular area of terrain. Defoliants are used to quickly kill vegetation and deny its use for cover and concealment. Chemical warfare can also be used against agriculture and livestock to promote hunger and starvation. Chemical payloads can be delivered by remote controlled container release, aircraft, or rocket. Protection against chemical weapons includes proper equipment, training, and decontamination measures.

History

Simple chemical weapons were used sporadically throughout antiquity and into the Industrial age. It was not until the 19th century that the modern conception of chemical warfare emerged, as various scientists and nations proposed the use of asphyxiating or poisonous gases. So alarmed were nations that multiple international treaties, discussed below, were passed banning chemical weapons. This however did not prevent the extensive use of chemical weapons in World War I. The development of chlorine gas, among others, was used by both sides to try to break the stalemate of trench warfare. Though largely ineffective over the long run, it decidedly changed the nature of the war. In most cases the gases used did not kill, but instead horribly maimed, injured, or disfigured casualties. Estimates for military gas casualties range from 500k to 1.3 million, with a few thousand additional civilian casualties as collateral damage or production accidents.
The interwar period saw occasional use of chemical weapons, mainly by multiple European colonial forces to put down rebellions. The Italians also used poison gas during their 1936 invasion of Ethiopia. In Nazi Germany, much research went into developing new chemical weapons, such as potent nerve agents. However, chemical weapons saw little battlefield use in World War II. Both sides were prepared to use such weapons, but the Allied powers never did, and the Axis used them only very sparingly. The reason for the lack of use by the Nazis, despite the considerable efforts that had gone into developing new varieties, might have been a lack of technical ability or fears that the Allies would retaliate with their own chemical weapons. Those fears were not unfounded: the Allies made comprehensive plans for defensive and retaliatory use of chemical weapons, and stockpiled large quantities. Japanese forces used them more widely, though only against their Asian enemies, as they also feared that using it on Western powers would result in retaliation. Chemical weapons were frequently used against Kuomintang and Chinese communist troops. However, the Nazis did extensively use poison gas against civilians in the Holocaust. Vast quantities of Zyklon B gas and carbon monoxide were used in the gas chambers of Nazi extermination camps, resulting in the overwhelming majority of some three million deaths. This remains the deadliest use of poison gas in history.
The post-war era has seen limited, though devastating, use of chemical weapons. Some 100,000 Iranian troops were casualties of Iraqi chemical weapons during the Iran–Iraq War. Iraq used mustard gas and nerve agents against its own civilians in the 1988 Halabja chemical attack. The Cuban intervention in Angola saw limited use of organophosphates. The Syrian government has used sarin, chlorine, and mustard gas in the Syrian civil war generally against civilians. Terrorist groups have also used chemical weapons, notably in the Tokyo subway sarin attack and the Matsumoto incident.
During the 2026 Iran massacres, reports from 17 January indicated the Iranian government may have used chemical weapons against protesters. Footage showed security forces atop vehicles wearing hazmat suits and masks designed for hazardous chemical materials. Some victims reportedly died several days after exposure rather than immediately. On 18 January, it was reported that the detained protesters were being injected with unknown substances while in custody. On 23 January, chemical gas was reported to have been used on the crowds of protesters and escape routes, causing severe breathing problems, burning pain of the eyes, skin and lungs, vomiting blood, and sudden weakness and loss of movement.
See also chemical terrorism.

International law

Before the Second World War

has prohibited the use of chemical weapons since 1899, under the Hague Convention: Article 23 of the Regulations Respecting the Laws and Customs of War on Land adopted by the First Hague Conference "especially" prohibited employing "poison and poisoned arms". A separate declaration stated that in any war between signatory powers, the parties would abstain from using projectiles "the object of which is the diffusion of asphyxiating or deleterious gases".
The Washington Naval Treaty, signed February 6, 1922, also known as the Five-Power Treaty, aimed at banning chemical warfare but did not succeed because France rejected it. The subsequent failure to include chemical warfare has contributed to the resultant increase in stockpiles.
The Geneva Protocol, officially known as the Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or other Gases, and of Bacteriological Methods of Warfare, is an International treaty prohibiting the use of chemical and biological weapons in international armed conflicts. It was signed at Geneva June 17, 1925, and entered into force on February 8, 1928. 133 nations are listed as state parties to the treaty. Ukraine is the newest signatory, acceding August 7, 2003.
This treaty states that chemical and biological weapons are "justly condemned by the general opinion of the civilised world". And while the treaty prohibits the use of chemical and biological weapons, it does not address the production, storage, or transfer of these weapons. Treaties that followed the Geneva Protocol did address those omissions and have been enacted.

Modern agreements

The 1993 Chemical Weapons Convention is the most recent arms control agreement with the force of International law. Its full name is the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction. That agreement outlaws the production, stockpiling and use of chemical weapons. It is administered by the Organisation for the Prohibition of Chemical Weapons , which is an independent organization based in The Hague.
The OPCW administers the terms of the CWC to 192 signatories, which represents 98% of the global population., 66,368 of 72,525 metric tonnes,, have been verified as destroyed. The OPCW has conducted 6,327 inspections at 235 chemical weapon-related sites and 2,255 industrial sites. These inspections have affected the sovereign territory of 86 States Parties since April 1997. Worldwide, 4,732 industrial facilities are subject to inspection under provisions of the CWC.